In the mining industry, blast holes are typically made with large diameter drilling equipment. The components of the drill rig are threaded and screwed together to transmit the force and the torque applied to the drill bit. During the drilling operation, intense dynamic effects are produced, with heavy shocks and vibrations that cause the threaded joint to stick. The situation worsens when the threads are damaged, or when the drill rig is used for long periods without disassembling.
The drilling equipment is typically fitted with hydraulic devices to loosen stuck joints, commonly known as breakout wrenches or chain wrenches. When they do not operate properly, the drilling is delayed, and several people with appropriate equipment have to work hard to loosen the joint, with significant risk for both people and equipment.
The typical cause of failure of the developed wrenches is insufficient gripping or dragging force between the clamps and the part being loosened, when the required loosening torque is high. This is due to the fact that the gripping force of the wrench over the piece is relatively constant, while the loosening torque varies from zero in the initial moment, up to the maximum value when the joint breaks. If the maximum required torque is higher than the torque allowed by the gripping force, the wrench slips over the stem and the operation has to be stopped.
To solve the problem, rig workers can apply heat to expand the part that has to be loosened, and deposit some bead welding to improve the dragging of the wrench, and then try again. The problem is often exacerbated when the stem is worn from use and thus has a reduced outside diameter.
In the search to solve the problem, it has been found, surprisingly, that when the gripping force increases with the applied torque, the slipping is substantially eliminated.
In a preferred embodiment of the present invention, the increase of the gripping force with the applied torque is achieved through a wrench where both the required torque and the gripping force of the clamps are produced simultaneously by the same hydraulic cylinder. This is attained by arranging the hydraulic cylinder in such a way as to produce the loosening torque through a lever that also generates the application force of the clamps. This effect is reinforced by the clamp design, which facilitates inlaying in the stem material to further reduce any slipping possibility.
In the case of a strongly stuck joint that requires a high loosening torque, the gripping force of the clamps over the component is equally high, with inlaying in the component, thereby allowing the hydraulic cylinder to be charged with a high pressure, if required, without slipping.
With this novel design we get in addition a great capacity to accommodate stems or components with different wear and different diameters, without any requirement of special adjustments. Thus, the wrench can be used with new stems, or with completely worn ones, with the smallest operating diameter, without any adjustment.